The hydrological cycle simulated by SWAT model is based on the water balance equation (Neitsch et al., 2002): This information, organized into database, is related to hydrology, weather, sedimentation, soil temperature, crop growth, nutrients, pesticides, ground water and lateral flow, and agricultural management. SWAT is a comprehensive model that requires a diversity of information in order to run. Hence, there are several available versions of SWAT, such as SWAT992, running under Windows.
This agrohydrological model was firstly used by Arnold in 1994 (Arnold et al., 1998), and it is in continual development and enhancement. This is the most complete and used model (Arnold et al., 1998 Neitsch et al., 1999 Neitsch et al., 2001 Neitsch et al., 2002). The SWAT simulation tool was developed to simulate the effect of alternative management decisions on water, sediment, and chemical yields with reasonable accuracy for ungaged basins. The model was used with success in several basins worldwide, primarily in United States and innmany European countries, like the Motueka basin (2075 km²) in New Zelande (Cao et al., 2003), the Alban Hills basin (1000 km²) in Central Italia (Benedini et al., 2003), the Celone Creek basin (24072 km²) in Italia (Papagello et al., 2003), and others. The model is the modification of the SWRRB model for application to large basins (Arnold et al., 1990). Jeff Arnold (1998) for USDA Agricultural Research Service (ARS). The SWAT (Soil and Water Assessment Tool) is a river basin, or watershed, scale model developed by Dr.
In general, procedures to estimate evaporation or evapotranspiration on a watershed basis rely, firstly, on an estimate of a potential E and ET (PE and PET), based on meteorological factors, and then conversion of the potential to an actual value for the watershed. The latter is one of the least understood aspects of the hydrologic cycle. The term includes evaporation of liquid water from rivers and lakes, bare soil and vegetative surfaces.Įvapotranspiration is the loss of water from soil and plant surfaces. Procedures for collecting and evaluating data are described in several references (Gray, 1970 Linsley, 1982).Įvaporation/evapotranspiration is a collective term for all processes by which water in liquid or solid phase, at or near the earth’s surface, becomes atmospheric water vapour.
Accurate calculation of precipitation is an essential input to the water balance, and careful attention must be paid to two areas in particular: Precipitation is the main input to the land-based component of the hydrologic cycle. Precipitation data is more widely available than streamflow data and is less affected by land-use changes.
The starting point for most water balance studies is the determination of a suitable precipitation series for the watershed.